The present invention generally relates to endoprostheses, also known as stents, and to their preparation and use. More particularly, the invention relates to endoprostheses having multiple junctions which join adjacent windings composed of undulating bendable segments which are oriented in a generally helical pattern along the length of the endoprosthesis. The bendable segments impart radial expandability to the endoprosthesis, which can be tailored so as to vary the hoop strength of the endoprosthesis while still retaining the ability of the endoprosthesis to follow the contour of the vessel within which it is to be deployed. Endoprostheses according to the invention also exhibit exceptional uniformity of expansion and maintain the desired solid surface area percentage substantially throughout the entirety of the endoprosthesis, particularly after deployment.
Various endoprosthesis devices or stents have been developed or proposed for use in association with angioplasty treatments and other medical treatments or procedures wherein devices having expandable components, such as balloon catheters, are used to treat a condition with a body vessel. The endoprosthesis or stent is in the nature of a device, usually tubular or cylindrical in shape, which is deployed by a balloon or otherwise, such as self-expansion, and which remains within the vessel at a treatment location upon withdrawal of the balloon catheter or other deployment and/or treatment device.
Exemplary patents in this regard include Pinchuk U.S. Pat. Nos. 5,019,090 and 5,092,877, MacGregor U.S. Pat. Nos. 4,994,071 and 5,015,253, Hillstead U.S. Pat. Nos. 4,856,516 and 4,913,141, and Gianturco U.S. Pat. Nos. 4,580,568 and 4,800,882. Certain endoprostheses or stents, such as those illustrated in Dotter U.S. Pat. No. 4,503,569, Wallsten U.S. Pat. No. 4,655,771 and Palmaz U.S. Pat. No. 4,733,665 present devices which have very limited compliance characteristics. They are not, for example, particularly well-suited for "stenting" body passageways having configurations which are not substantially linear. For example, stenting curved vessel pathways with endoprostheses that present a generally rigid cylindrical shape typically requires endoprostheses that are very short in length and that are strung out along the curved pathway, with each such endoprosthesis engaging an adjacent endoprosthesis along respective edges of the endoprostheses, thereby leaving a gap between each pair of endoprostheses at the outside radius of the curved vessel being stented. Also, such endoprostheses often will be delivered separately, thereby increasing the invasiveness of the procedure. In other endoprostheses, concerns can be raised that the body of the endoprosthesis stretches along its longitudinal axis during use. For example, Wiktor U.S. Pat. No. 5,133,732 proposes longitudinal over-stretch limiting means such as by attaching a longitudinal wire generally parallel to the axis of the endoprosthesis.
Accordingly, previous approaches in the endoprosthesis or stent art have proposed or provided devices having good hoop strength, which can be particularly important in stenting applications which could be subjected to forces tending to collapse the endoprosthesis, such as when relatively large vessels are stented or when the stent is deployed within a vessel susceptible to external forces, such as within the leg. Other known endoprostheses or stents exhibit less hoop strength but are more compliant in that they are better suited to conform to the contour of the vessel, rather than being so non-conforming as to mis-shape the vessel after deployment. A typical disadvantage of the more-compliant stent devices is that they tend to deform upon or after deployment and present stenting surfaces which can lack desirable uniformity throughout the working surface area of the stent. Development of non-uniformity in the working surface area of the stent can be especially evident during expansion of the stent from its collapsed, insertion diameter to its expanded, implanted diameter. At times, for balloon-deployed stents, this lack of uniformity upon expansion is exacerbated by folds or other non-uniformities in a balloon on which the stent is mounted for deployment.
It has been found that the endoprostheses in accordance with the present invention exhibit the ability to follow the contour of the vessel being stented while still exhibiting the hoop strength needed for adequate support such as that provided by less compliant structures including those as discussed herein, while providing the additional advantage of ensuring uniform expansion to provide an expanded stent that exhibits the desired percentage of support surface area. Furthermore, with the present invention, these important properties can be tailored to fit the particular needs of the problem being addressed by varying compliance and hoop strength as needed.
In summary, the present invention achieves these advantages and advances the endoprosthesis art by an endoprosthesis constructed of a plurality of bendable segments organized in an undulating and substantially uniform fashion having a generally helical configuration. The endoprosthesis body is thus composed of a plurality of full-circle undulating sections continuous with each other along the helical path. In general, the undulations of adjoining full circle sections generally line up with one another to either contact one another or be closely spaced from one another. At selected ones of these locations, bridges are provided in order to thereby join adjacent sections. At least one bridge is positioned along each full-circle section. In an especially preferred embodiment, the bridges are oriented with respect to each other so as to form a helical pattern of bridges along the endoprosthesis.
It is accordingly a general object of the present invention to provide an improved endoprosthesis having multiple bridged junctions and to make and use same.
Another object of the present invention is to provide an improved endoprosthesis or stent that exhibits good strength while having the ability to follow the contour of the vessel within which it is implanted.
Another object of this invention is to provide an improved endoprosthesis that minimizes the risk of developing intimal hyperplasia or irritation brought on by its deployment within a living vessel and the method associated therewith.
Another object of the present invention is to provide an improved endoprosthesis and deployment procedure whereby the stent overlaps by at least about 0.5 cm both sides of a dissection being treated, even in the case of an elongated dissection that does not exhibit a straight contour.
Another object of this invention is to provide an improved endoprosthesis and method to provide a stent which has an integrity comparable to that of a much less flexible stent while still exhibiting flexibility required in many uses, including within coronary vessels.
Another object of the present invention is to provide an endoprosthesis having multiple bridged junctions which exhibit a flexibility reduced by only about 10 to 15% of a similar device without bridged junctions and while simultaneously providing the integrity of stent structures exhibiting much less flexibility or compliance properties.
Another object of this invention is to provide an improved stent or endoprosthesis and use thereof with exceptional uniformity in presentation of supporting surface area throughout the working surface of the stent.
Another object of the present invention is to provide an improved endoprosthesis or stent which reduces in length when expanded during deployment, while increasing the pitch of the helix that broadly defines the configuration of the endoprosthesis.
Another object of the present invention is to provide an improved endoprosthesis or stent which, when deployed, avoids overlap of stent structural components to thereby provide a stent having minimal thickness throughout the stent to reduce the likelihood of accelerated hyperproliferation or thicker cell growth as a protection response to a thickened wall surface.
Another object of the present invention is to provide endoprostheses and manufacture thereof while tailoring same for desired end uses, including vascular, bronchial, tracheal, urological, rectal, transinterhepactic shunting, bilary tree, and the like.
Another object of this invention is to provide an improved endoprosthesis having multiple bridged junctions which substantially reduce external expansion of a stent when deployed within vessels having curved contours.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.